Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the annotations (readOnlyHint=false, destructiveHint=false, openWorldHint=true, idempotentHint=false), the description discloses that the result is a new version rather than an in-place overwrite ("Returns a link to the new version plus Mermaid code where available") and that the call costs 1 AI credit. These are cost and output-shape facts not derivable from the structured fields, and the "new version" framing is consistent with destructiveHint=false.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three sentences, all front-loaded: capability first, inputs second, output/cost last. The operation list is dense but each item conveys a distinct capability rather than padding.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a two-parameter mutation tool with no output schema, the description covers everything an agent needs: the required input format, the natural-language change instruction, the return value (link plus Mermaid where available), and the credit cost. No meaningful gap remains.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so both parameters are already documented; the description reinforces the diagram argument as the import link and stresses that the instruction is "plain English," which clarifies the expected natural-language input format. It adds modest meaning rather than new constraints, so it sits just above the baseline for fully covered schemas.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb+resource ("Change a diagram made earlier in this chat") and enumerates the concrete operations available (add/remove/rename/reconnect steps, shorten labels, recolour, restructure). It explicitly contrasts with create_diagram, so an agent can distinguish it from siblings like render_diagram or code_to_flowchart without inspecting schemas.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

States the selection rule outright: "Use this instead of create_diagram whenever the user wants to adjust a diagram they already have, so their earlier work is kept." It names the alternative tool and the condition that selects it, which is exactly what an agent needs to route correctly.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.